Apparatus such as document and film scanners having linear image sensing arrays to produce an electronic image signal by sensing the original a line at a time, employ linear light sources to illuminate the original one line at a time. U.S. Pat. No. 4,186,431 issued to Engel et al., Jan. 29, 1980, shows a linear light source for use in a document scanner. The light source comprises an elongated incandescent lamp inside a specularly reflective tube. The reflective tube is provided with a slit to emit a line of light, and a light diffusing strip over the slit to produce a pattern of uniform intensity along the slit.
For a film scanner, operating at normal film projection rates, e.g. 24 frames per second, an intense uniform source of light is required. For optimum scratch suppression, it is also desirable for the light to be diffuse and nearly uniform in angular distribution (i.e. Lambertian). The straight line light source described in U.S. Pat. No. 4,186,431 suffers from the drawback that the incandescent light source is not as bright as desired for a high resolution film scanner and does not have the best color temperature for scanning color film. Intense light sources such as Xenon arc lamps and lasers are not produced in a linear configuration like the elongated incandescent lamp. Furthermore, the intensity distribution produced by the light source can be improved.
It is therefore the object of the present invention to provide apparatus for producing a line of illumination that is free from the shortcomings noted above.